With the puzzle, looking at the number 8 first, the only options for 8 to go in the bottom right square is C7R7, C7R9, C9R7 and C9R9.
C7R7 and C7R9 can be ruled out as C6R7 and C6R9 are not highlighted, and putting an 8 in C7R7 and C7R9 would cause them to have repeated orthogonal neighbours.
As now the only options for 8 to place in the bottom right square is C9R7 and C9R9, the only place to put 8 in the middle right square is C7R5. The problem with that is that there is an 8 in C2R2. Hence I think this puzzle is unsolvable
Could someone please look into this?